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Name: Kaleb
Status: student
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Question:
Why do closer objects look as if they are moving faster than further objects, when travelling in a car?


Replies:
The answer to your question is not only a physics question, but also a biology and psychology question. It deals with how we perceive... how we interpret what we sense.

Our perception of speed is a function of how fast an image moves across the retina of our eye. If two objects - one near and one far - moving at the same speed, will be perceived differently. The near one will cross our field of vision more quickly than the far one and therefore will be judged as moving faster.

A baseball pitch look a lot faster to the batter than to the fan in the stands. The closer you sit to racetrack, the faster the race car seems to move. An airplane making a contrail in the sky looks to be moving rather slow when it is really doing over 500 mile per hour. It could be as much as eight miles in the sky.

Larry Krengel


Neat question, Kaleb.

The faster something makes us turn our head or shift our eyes to follow it, the faster our brain says it is moving. We learn this at a very early age and no one needs to teach us. We learn form our own experience!

To watch something near the car as we go by, means we have to move our head and/or eyes quickly to keep it in view. So, our brain says, "This is moving quickly".

We can look at something far away, such as a jet or mountains, a long time without moving our head or eyes. The brain says, "That is far away".

And, of course, our brain says everything else is moving as we drive along, not us. Our brains cam about long before humans ever got around to travelling as fast as we do in a car. I guess you could say, our brains need to play catch - up.

Hope this helps.

Robert Avakian


Kaleb

In the attached drawing, all of the items in drawing A and in drawing B are the same size. The figure in drawing A is farther away from the eye than the figure in drawing B.

If you look at the drawing analytically, you can see that the angle from the horizontal line to the top of the figure in drawing A is smaller than the same angle in drawing B.

So as the figure comes closer to the eye, the bigger the figure looks, the larger the angle gets, the faster the angle increases, and the faster it looks like the figure is traveling.

The reverse is true of a figure that is moving farther away. The farther away the figure gets, the smaller it looks and the slower it looks.

Sincere regards,

Mike Stewart


Hi Kaleb,

The answer to this one uses the geometry of circles. One way you gauge speed of an object is by how fast you have to rotate your eyes or head to keep looking at the object. You can think of the object as moving around the perimeter of a circle with you at the center. The radial speed (degrees or radians per second) equals the linear speed (distance per second) divided by the radius (distance). The larger the radius (the larger the distance from you), the slower the radial speed that you have to move your head (and therefore the slower the object appears to be traveling) to keep your eyes on the object.

Another, perhaps smaller, factor is that at a longer distance, your eyes cannot make out as fine details, so the background objects that moving object passes are less clear. With closer objects, you can see smaller objects in the background, and the object moving past them gives you the perception of faster speed.

Hope this helps,

Burr Zimmerman


Kaleb,

There are two reasons for this fact. In American society, the first probably has the greater effect:

This is partially due to the training we receive by watching movies. We know an object getting larger is getting closer. An object at a distance does not appear to grow as quickly as does a close object. I have been told of an experiment done to compare those raised on movies and television to those that had never seen such things. If I recall correctly, the movie was a solid-colored circle on a solid-colored background. The circle grew at a steady rate, quickly enough to look like a ball flying at the viewer's face. Those that had watched movies all their lives described it as a ball moving toward them. Those never exposed to movies described it as a circle getting larger.

Another reason relates to standards. We tend to compare things we see to those around us. Unless trained to do so, our first intention is to describe something as "twice as far" as something else. An object moving at one meter per second at 100 meters will travel ten meters in ten seconds. This is ten meters out of one hundred: one part in ten. An object at only ten meters travels one part in ten, or one meter out of ten meters, in only one second.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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